The wheel of the car, for example, is supported rotatably by the suspension system via the double row angular contact rolling bearing unit. Also, in order to secure the running stability of the car, the vehicle running stabilizing system such as the anti-lock brake system (ABS), the traction control system (TCS), the vehicle stability control system (VSC), or the like is employed. In order to control various vehicle running stabilizing systems, various signals such as a rotation speed of the wheel, accelerations applied to a car body in respective directions, and the like are needed. Then, in order to execute the higher control, in some cases it is preferable to know the magnitude of the axial load applied to the rolling bearing unit via the wheel.
In view of such circumstances, the load measuring unit for the rolling bearing unit shown in FIG. 5 is recited in JP-A-3-209016 (referred to as “Patent Literature 1” hereinafter). First, the configuration of the conventional system will be explained hereunder. A rotary-side flange 2 for supporting the wheel is fixed to an outer peripheral surface of an outer end portion (here, the “outside” in the axial direction denotes the out side in the width direction of the car body in a state assembled to the car, and also corresponds to the left side in FIGS. 1, 2, 5) of a hub 1, which is a rotary ring and also is an inner ring equivalent member. Also, double row inner ring raceways 3, 3 are formed on an outer peripheral surface of a middle portion and an inner end portion (here, the “inside”) in the axial direction denotes the middle side in the width direction of the car body when assembled to the car, and also corresponds to the right side in FIGS. 1, 2, 5) of the hub 1.
Meanwhile, a stationary-side flange 6 for supporting/fixing an outer ring 4 onto a knuckle 5, which constitutes the suspension system, is fixed to an outer peripheral surface of the outer ring 4, which is arranged around the hub 1 concentrically with the hub 1 and serves as a stationary ring. Also, double row outer ring raceways 7, 7 are formed on an inner peripheral surface of the outer ring 4. A plurality of balls 8, 8 acting as the rolling elements are provided rotatably between the outer ring raceways 7, 7 and the inner ring raceways 3, 3 respectively, so that the hub 1 is supported rotatably on the inner diameter side of the outer ring 4.
In addition, a load sensor 11 is affixed to plural portions, each of which surrounds a respective threaded hole 10, on the inner surface of the stationary-side flange 6. Bolts 9 for fitting the stationary-side flange 6 to the knuckle 5 are screwed into the threaded holes 10. These load sensors 11 are held between an outer surface of the knuckle 5 and the inner surface of the stationary-side flange 6 so that the outer ring 4 is supported/fixed to the knuckle 5.
In such a load measuring unit as known in the prior art, when the axial load is applied between the wheel (not shown) and the knuckel 5, the outer surface of the knuckle 5 and the inner surface of the stationary-side flange 6 press strongly the load sensors 11 mutually from both sides in the axial direction. Accordingly, the axial load applied between the wheel and the knuckle 5 can be sensed by summing up the measured values of these load sensors 11.
In the case of the conventional configuration shown in FIG. 5, the load sensors 11 must be provided as many as the bolts 9 that support/fix the outer ring 4 to the knuckle 5. As a result of above situation along with the fact that the load sensor 11 itself is expensive, it is unavoidable that a cost of the overall load measuring unit for the rolling bearing unit is considerably increased.
The present invention is made in view of such circumstances to implement such a configuration that can be constructed at a low cost and also can measure an axial load applied to each wheel while keeping an accuracy required for control.